1. Field of the Invention
The present invention relates to a printing apparatus, a printing method, and a computer program.
2. Description of the Related Art
An inkjet printer performs a rendering process in which input image data is converted into output image data, while the print head of the inkjet printer performs scanning along the main-scanning direction. Such a rendering process, however, requires a long time. In particular, when an A0-sized image is to be printed, the rendering process takes longer time than when an A4-sized image is printed. Recently, there is an increasing demand for a higher linear velocity in large-sized printers which is capable of printing A0-sized images. Therefore, it is desirable that the rendering process be performed in higher speed.
To improve printing quality, an inkjet printer performs printing in multi-pass print mode, in which the head scans a target a plurality of times to finish printing of a single image in the main-scanning direction, or interlaced print mode, in which the head scans the target a plurality of times to finish printing of a single image in the sub-scanning direction. The extended length of time required in the rendering process becomes more prominent when the multi-pass print mode or the interlaced print mode is selected.
Thus, in one known conventional technology, an image is compressed to data of such an amount that can be output by scanning the target with the print head only once. This data is stored in a memory as intermediate data. Thus, the amount of image data to be processed is reduced and the time required for rendering is also reduced.
In addition, Japanese Patent Application Laid-open No. 2006-209458 discloses a technology for realizing a high speed rendering process. According to this technology, effective data is read out from an input image data stored in a memory in an interlacing process, and only the effective data is packed in an intermediate data generating process.
However, in such conventional technologies, when a printing process is performed in the multi-pass print mode, some data is lost during image compression, which is performed for generating the data to be output in a scanning by one print head. This lost data, however, needs to be read out again from the memory for generating data to be output in a scanning by another print head. More specifically, the input image data stored in one memory area is read out, and the read-out data is compressed to 1/(the number of passes). The compressed data, i.e., intermediate data is stored in another memory area. The data lost in the compression, i.e., a part of the input image data is required for generating the data to be output in the scanning by another print head. Hence, for generating the data to be output in the scanning by this another print head, the same input image data has to be read out again. Thus, the speed of rendering process lowers.
In the technology according to Japanese Patent Application Laid-open No. 2006-209458 as well, the input image data has to be read more than one time, thus reducing the processing speed of the rendering process.